From: Artem Savkov <asavkov@redhat.com>
Date: Tue, 20 Nov 2018 11:52:16 -0600
Subject: objtool: Fix segfault in .cold detection with -ffunction-sections
Git-commit: 22566c1603030f0a036ad564634b064ad1a55db2
Patch-mainline: v4.20-rc5
References: bsc#1058115

Because find_symbol_by_name() traverses the same lists as
read_symbols(), changing sym->name in place without copying it affects
the result of find_symbol_by_name().  In the case where a ".cold"
function precedes its parent in sec->symbol_list, it can result in a
function being considered a parent of itself. This leads to function
length being set to 0 and other consequent side-effects including a
segfault in add_switch_table().  The effects of this bug are only
visible when building with -ffunction-sections in KCFLAGS.

Fix by copying the search string instead of modifying it in place.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 13810435b9a7 ("objtool: Support GCC 8's cold subfunctions")
Link: http://lkml.kernel.org/r/910abd6b5a4945130fd44f787c24e07b9e07c8da.1542736240.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 tools/objtool/elf.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -31,6 +31,8 @@
 #include "elf.h"
 #include "warn.h"
 
+#define MAX_NAME_LEN 128
+
 struct section *find_section_by_name(struct elf *elf, const char *name)
 {
 	struct section *sec;
@@ -298,14 +300,23 @@ static int read_symbols(struct elf *elf)
 	/* Create parent/child links for any cold subfunctions */
 	list_for_each_entry(sec, &elf->sections, list) {
 		list_for_each_entry(sym, &sec->symbol_list, list) {
+			char pname[MAX_NAME_LEN + 1];
+			size_t pnamelen;
 			if (sym->type != STT_FUNC)
 				continue;
 			sym->pfunc = sym->cfunc = sym;
 			coldstr = strstr(sym->name, ".cold");
 			if (coldstr) {
-				coldstr[0] = '\0';
-				pfunc = find_symbol_by_name(elf, sym->name);
-				coldstr[0] = '.';
+				pnamelen = coldstr - sym->name;
+				if (pnamelen > MAX_NAME_LEN) {
+					WARN("%s(): parent function name exceeds maximum length of %d characters",
+					     sym->name, MAX_NAME_LEN);
+					return -1;
+				}
+
+				strncpy(pname, sym->name, pnamelen);
+				pname[pnamelen] = '\0';
+				pfunc = find_symbol_by_name(elf, pname);
 
 				if (!pfunc) {
 					WARN("%s(): can't find parent function",